In contrast to fossil fuels, the combusting of biofuels in principle gives no contribution of carbon dioxide to the atmosphere. The amount of carbon dioxide that is formed during the combustion is exactly the same amount that the plant has assimilated during its growth, and as long as the fresh growth is as large as the extraction, the carbon dioxide content in the atmosphere will not increase. Consequently, in case the use of biofuels suddenly increases, the carbon dioxide content into atmosphere will increase temporarily, until the biomass can grow back and compensate for the emissions.
In this manner, the use of biofuels will deliver rather large amounts of carbon dioxide for 20-30 years ahead (until 2030-2040), since the firing of biofuels has increased largely during the latest decennium and probably will continue to increase during the twenty-tens. Researchers from SLU (the Swedish University of Agricultural Sciences) and IVL (the Swedish Environmental Institute) have shown in a report from Elforsk (Report No. 07:35) that firing of bio fuel probably is more climate affecting than if natural gas were used for covering the same energy demand during the next 20 years. That bio fuel in spite thereof is regarded as carbon dioxide neutral is based on that the use is viewed from a 100 years approach and that the use is maintained constant or is reduced.
Bio fuels are used for generation of electricity and heat and for motor fuels. In countries having a developed pulp and paper industry, like Sweden, Finland and Canada, this industry accounts for a major portion of the use.
Usual biofuels are tree fuels, spent liquors in the pulp industry, and refuse. Tree fuels come from raw material of wood and may be firewood, logging waste (stumps, branches, tops and bark, et cetera), for example, or energy forest. Another very common bio fuel is the mixture of chemicals and dissolved organic material formed at chemical pulp mills, often called spent, waste or residual liquor or in most cases black liquor. The liquor is combusted at the mill and is an important source for both heat and electricity.
Biodiesel is the name for a motor fuel, which till now has been produced by transesterification of vegetable oil or esterification of fats, but biodiesel may also be produced by hydrogenation of primarily fats and vegetable oils. Sometimes also the designation FAME (Fatty Acid Methyl Ester) is used for biodiesel. In principle any type of fat can be used for production of biodiesel. The choice is mainly decided by price and availability of the raw material. In Sweden, rapeseed is most common, and then the fuel is called RME (Rapeseed Methyl Ester). In the U.S., most often soybean oil or maize oil is used. Also palm oil, mustard oil or algae may be used. The transesterification is started by adding methanol or ethanol and alkali in the presence of a catalyst to obtain monoalkyl esters and glycerol, which are removed.
Consequently, upon producing biodiesel, glycerol (also known as glycerin, propane-1,2,3-triol, trihydroxy-propane, CH2OH—CHOH—CH2OH) is obtained as a byproduct. This has lead to that the yearly production of glycerol in the U.S. in recent years has amounted to 350,000 tons and in Europe 600,000 tons. These figures will increase by the implementation of the E.U. Directive 2003/30/EC, which requires that 5.75% of the petroleum fuels be replaced by bio fuels in all states.
In HU 0001665 A2 there is disclosed a proposition to combust byproducts from production of biodiesel, e.g. sun flower husks and contaminated glycerol, together to produce energy.
US 2004/0159042 A1 discloses a biofuel product formed by a mixture of a powder, which may be either a dried cellulose containing product, powder of charcoal, and/or a combination thereof and a liquid, which may be a vegetable oil, vegetable alcohol or a combination thereof. Vegetable oil is glycerol esters, and the oil molecule consists of three carboxylic acids residues attached to a glycerol molecule. As glycerol makes the oil thick and sticky, in order to be transformed into a fuel, the oil must go through a transesterification process, whereby the esters are separated from the glycerol and alcohol is substituted for the glycerol. The vegetable alcohols used for this purpose are ethanol and ethanol. The oil and/or the alcohol or a mixture thereof is used in form of microdrops for moistening the powder. It is stated that by mixing 5-10 gallons (18.9-27.8 liters) of biodiesel per ton of dry powder, a biofuel product is obtained, which is in a liquid cream state and may serve as a replacement for or additive to conventional liquid fossil fuels, such as for heating purposes.
Further, it is proposed in U.S. Pat. No. 7,195,656 B2 to reduce emissions of NOx when combusting pulverized coal by co-firing an oxygen containing compound selected from the group consisting of glycerol, glycerol derivates, propylene glycol, propylene glycol derivates, ethylene glycol, ethylene glycol derivates, fatty acid alkyl esters, fatty alcohols, and mixtures thereof. Concerning glycerol, it is typically obtained as a byproduct when producing soaps, fatty acids, fatty alcohols and alkyl esters. Another possible source is stated to be from the hydrogenation or the enzymatic conversion of glucose, sorbitol and other sugars to glycerine or other polyols. Yet another source is waste products of ethanol fermentation. Synthetic glycerol may also be obtained from propylene, typically in Dow Chemical's process for production of epichlorohydrin from allyl chloride. Also all in all, this does not add up to a large amount of glycerol that is desirable to utilize. In addition, even if the glycerol would be mixed with the pulverized coal, no bio fuel product harmless to the environment would be obtained, since coal is a fossil fuel that contributes to increased carbon dioxide emissions.